In Dante Alighieri's Dante's Inferno (or The Divine Comedy), a narrative epic poem, the main theme is good versus evil.
It is important to note that this tale is not a "comedy" by modern standards. Instead, Dante's title is based upon the medieval definition of a story with "a happy ending." Dante must travel through three realms, on three journeys: to Hell, Purgatory and Paradise. "Inferno" refers to the first realm: Hell as presented through Alighieri's Christian beliefs.
The main plot thread is that Dante has lost his way in life—the play begins on Holy Thursday (the night before Good Friday). Beatrice begs Virgil (the ancient Roman poet) to find Dante, which he does on the night of Good Friday. Dante and Virgil enter Hell and proceed to the nine circles of Hell (believed to be found within the earth). It is here that sinners are placed based upon the nature of their misdeeds: lust, gluttony, flatterers, hypocrites, thieves, etc. Lesser sins (e.g., lust and anger) are placed at the top of the circle, while the lower circles are reserved for the truly evil (e.g., traitors and liars)—movement down the circles showing a "gradual increase in wickedness."
The Romans closely followed the Greeks in organizing their society except for their definition of sin.
The Greeks felt that a violent act against another human being was the worst form of evil.
However, for the Romans, deceit and treachery (treason) were the most abhorrent. It was the Roman model that Dante followed in his epic tale.
Dante's journey ends on Easter: he has seen heavenly justice carried out through the punishment of sinners, and finally finds his way back to God.
In the midst of this rests the struggle between good and evil (sin). Dante, in the middle of his life, finds he has fallen off of the straight ("right") path—the one that leads to Heaven through salvation. As Virgil and Dante move through Hell, Dante discovers that the punishment for each sin is a form of each soul's original sin—where the sinner finds "poetic justice." We might see their punishments as ironic. For example, trying to divine [tell] the future was considered a sin.
[F]ortune-tellers have to walk forward with their heads on backward, unable to see what is ahead, because they tried to see the future through forbidden means.
And so, the sin committed becomes part of the punishment for that sinner. As Dante enters through Hell's gate, he sees the now-famous line, inscribed there:
Abandon all hope, ye who enter here.
This reflects the loss hope (of God's forgiveness and grace) in living a life of sin—being in a place where, from a theological standpoint, God is absent. The sense of doom and punishment rests in this place: where one goes with sins resting fully on his soul. Ironically, there is also a place here for those whose sin was doing nothing. A famous figure found here is Pontius Pilate who relinquished the fate of Jesus Christ to Jewish law, wiping his hands clean of any responsibility—though by Roman law, Pilate noted Jesus had done nothing wrong. Also there are angels who did not act at all during Satan's rebellion (the Rebellion of Angels). These details show a difference between purposely committing sin through one's actions, and committing sin by inaction.
The fact that the story takes place over Holy Week (Holy Thursday through Easter Sunday) is no coincidence. These are dates on the Christian calendar that far exceed others in importance—even Christmas. For while Christmas is holy in that it celebrates the birth of Christ, it is his crucifixion—his sacrifice of self for the sins of all mankind—around which the Christian faith revolves. For while Jesus' birth is of great importance, for a Christian it is only stands out in relation to Christ's death and resurrection: it is seen as the single act that delivers mankind from hell—where non-believers are believed to go—because of their sins.
With this said, the Inferno represents the place of punishment. The other parts of the Comedy bring Dante to a place of renewal of faith and into a place of grace for striving to battle evil with a belief in, and commitment to, goodness above sin. Dante's Inferno shows the Christian belief that the result of sin is suffering in Hell. It also shows that a commitment to lead a God-centered life is rewarded with a place in Heaven after death.